12
Chapter 12
Client/Server Systems
Database Systems: Design, Implementation, and
Management, Fifth Edition, Rob and Coronel
12
In this chapter, you will learn:
• What client/server computing is
• What the advantages of using client/server
systems are
• How client/server systems evolved
• About client/server systems components and
how they interact
• What effect the client/server system has on the
DBMS
• How client/server systems might be introduced
into an organization
• What factors affect the implementation of
client/server systems
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
2
12
Client/Server Computing
• Computing model for the development of
computerized systems
– Client requests specific service
– Server provides requested service
• Reside on same or different computers
Figure 12.1
Database Systems: Design, Implementation, & Management,
5th
Edition, Rob & Coronel
3
12
Client/Server Computing (con’t.)
• Key to client server power is where request
processing takes place
• Extent of sharing processing
–
–
–
–
Thin client
Thin server
Fat client
Fat server
• Classification
– 2-tier
– 3-tier
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
4
12
Forces that Drive Client/Server Trend
• Changing business environment
• Growing need for enterprise data access
• Demand for end-user productivity gains based on
efficient use of data
• Technological advances
• Growing cost/performance advantages
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
5
12
Evolution of Computing Environment
Figure 12.2
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
6
12
Mainframe vs. Client/Server Systems
Table 12.1
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
7
12
Managerial Expectations of
Client/Server Systems
• Client/Server efficiency functions
– Platform independent development
– Optimized distribution of processing activities
among different platforms
– User friendly and cost effective techniques,
methodologies, and specialized tools
• Observations
– Tool, not end goal
– Not answer to all data management problems
– Has own set of management problems
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
8
12
MIS Expectations of
Client/Server Benefits
• Reduced development and implementation costs
• Reduced development time and increased
programmer productivity
• Extended system life cycle through scalability
and portability
• Reduced system operational cost
• Change of MIS function from development to enduser support
• Enhanced information deployment
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
9
12
Organizational Expectations of
Client/Server Benefits
• Flexibility and adaptability
• Improved employee productivity
• Improved company work flow and way to
reengineer business operations
• New opportunities for competitive advantages
• Increased customer service satisfaction
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
10
12
Components of
Client/Server Architecture
• Client
– Front-end application
• Server
– Back-end application
• Communications middleware
– Communications layer
Figure 12.3
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
11
12
Example Client/Server Architecture
Figure 12.4
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
12
12
Client/Server Principles
• Hardware independence
• Software independence
– Operating systems
– Network systems
– Applications
• Open access to services
• Process distribution
–
–
–
–
Process autonomy
Maximization of local resources
Scalability and flexibility
Interoperability and integration
• Standards
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
13
12
Server Components
•
•
•
•
•
•
•
File services
Print services
Fax services
Communications services
Database services
Transaction services
Miscellaneous services
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
14
12
Server Components
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
Figure 12.6
15
12
Typical Characteristics of
Server Hardware
• Fast CPU
• Fault-tolerant capabilities
–
–
–
–
Dual power
Standby power
Error checking and correcting memory
RAID
• Expandability of CPU, memory, disk, and
peripherals
• Bus support for multiple add-on boards
• Multiple communications options
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
16
12
Server Process Benefits
•
•
•
•
Location independence
Resource optimization
Scalability
Interoperability and integration
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
17
12
Database Middleware
• Network independence
– Front-end application accesses data without
regard to network protocols
• Database server independence
– Generic SQL to access different database servers
– Isolates programmer from SQL dialect differences
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
18
12
Communications Middleware
• Two levels
– Physical level
• Client and server computers
– Logical level
• Client and server processes
• Interprocess communication (ICP) protocols
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
19
12
OSI Network Reference Model
Table 12.2
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
20
12
Information Flow through OSI Model
Figure 12.7
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
21
12
Transport Process ID
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
Figure 12.8
22
12
Network Protocols
• Transmission Control Protocol/Internet
Protocol (TCP/IP)
• Internetwork Packet Exchange/ Sequenced
Packet Exchange (IPX/SPX)
• Network Basic Input Output System
(NetBIOS)
• Application Program to Program
Communications (APPC)
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
23
12
Database Middleware Components
Figure 12.9
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
24
12
Interactions between
Middleware Components
Figure 12.10
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
25
12
Middleware Accessing Multiple
Database Servers
Figure 12.11
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
26
12
Middleware Accessing Mainframe
Databases
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
Figure 12.12
27
12
Middleware Classifications
• Messaging-oriented middleware (MOM)
• Remote-procedure-call-based (RPC-based)
middle ware
• Object-based middleware
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
28
12
Competing Standards
• Client operating systems
– Microsoft Windows
– OS/2, Apple Mac OS, Unix, Linux
• Client graphical user interfaces
– Microsoft Windows
– OS/2 Presentation Manager, Macintosh, UNIX
• Server operating systems and network
protocols
– Database servers: Unix, OS/2, Windows NT
Server/2000 Server
– Printer and file servers: Novell Netware
– LAN protocols: TCP/IP, IPX/SPX, NetBIOS
• Middleware
– ODBC, IDAPI, DRDA, Q+E
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
29
12
Client/Server DBMS Functions
• Transparent data access to multiple,
heterogeneous clients
• Allow client requests to the database server over
network
• Process client data requests at local server
• Send only SQL results to clients over network
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
30
12
Application Logic Components
Figure 12.14
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
31
12
Client/Server Architectural Styles
• Two Key Questions
– How is the division made?
– Where should the results of division be placed?
• Five Functional Logic Components
–
–
–
–
–
Presentation logic
I/O processing logic
Application of business logic
Data management logic
Data manipulation logic
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
32
12
Application Functional Components
Figure 12.15
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
33
12
Functional Logic Splitting
Figure 12.16
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
34
12
Client/Server versus Traditional DP
• Proprietary to open systems
• Maintenance-oriented coding to analysis, design,
and service
• Data collection to data deployment
• Centralized to distributed style
• Vertical, inflexible to horizontal, flexible
organizational style
• Differences in IS components
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
35
12
Client/Server Implementation Issues
• Management Issues
–
–
–
–
–
Communications infrastructure
Applications
Controlling escalating and hidden costs
People and cultural changes
Multiple vendor relationships
• Development tool acquisition
• Determination if client/server approach is correct
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
36